1. Field of the Invention
The present invention relates to a marine propulsion machine including a driving mechanism rotatively driven by an engine, an output gear mechanism driven by the driving mechanism, and a propeller shaft driven by the output gear mechanism.
2. Description of the Related Art
There has been known a marine propulsion machine provided with a driving mechanism that drives an output gear mechanism for driving a propeller shaft. The driving mechanism includes a first drive shaft operatively connected to an engine, an intermediate gear mechanism driven by the first drive shaft, and a second drive shaft rotatively driven by the gear mechanism. A bearing supporting the second drive shaft is disposed immediately below a driven gear included in the intermediate gear mechanism (see, for example, JP-A 3-21589 or JP-A 63-97489).
When the bearing supporting the second shaft interlocked with the first drive shaft by the intermediate gear mechanism is disposed immediately below the driven gear, the second drive shaft needs to have an upper end part, on which the driven gear is mounted, extending upward from the bearing. Consequently, the second drive shaft is long and heavy and troublesome work is needed to install the bearing under the driven gear. When bearings are disposed immediately below and immediately above the driven gear, respectively, the number of parts, assembling work and the cost increase.
When an oil pump is driven by the intermediate gear mechanism, the capacity of the oil pump is subject to the reduction ratio of the intermediate gear mechanism, and resistance to the oil-stirring motion of the intermediate gear mechanism causes a large power loss. When the oil pump is driven by the second drive shaft that rotates at a reduced rotational speed lower than the rotational speed of the first drive shaft, the oil pump needs to have a large capacity to discharge oil at a desired discharge rate. Such an oil pump having a large capacity is large in bulk and, in some cases, it is difficult to secure a large space for the large oil pump. When the oil discharged from the oil pump is used for lubricating moving parts held in a gear case, it is desirable to form oil passages without enlarging the gear case.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a marine propulsion machine provided with a driving mechanism including a first drive shaft, a second drive shaft and an intermediate gear mechanism interlocking the first and the second drive shaft, in which a structure related with a bearing supporting the second drive shaft is designed to configure the second drive shaft in a short length and a small weight and to manufacture the second drive shaft at a low cost.
Another object of the present invention is to provide a machine propulsion machine including an oil pump, in which the freedom of determining the capacity of the oil pump is high, the oil pump is small, power loss resulting from the resistance of oil to stirring the oil is reduced, a gear case is formed in a small size by forming oil passages for the oil discharged from the oil pump in the gear case.